The invention concerns a method for detecting a hot start situation in an internal combustion engine of a motor vehicle. The invention also concerns an appropriate electronic control unit for an internal combustion engine, an appropriate computer program with program code means, and an appropriate computer program product with program code means.
In general, a hot start situation exists, e.g., when an internal combustion engine that is still hot is restarted after a short pause in operation. When a hot machine is at rest, fuel vapor bubbles form in the fuel lines and in the injection valve itself. When said machine is then started, these fuel vapor bubbles inhibit regular fuel metering. For this reason, an extended injection signal is output under hot start conditions, so that a certain minimum amount of fuel can be provided to the combustion process even when fuel vapor bubbles occur. It is therefore necessary to determine when a hot start situation exists.
Publication DE 40 39 598 A1 discloses a hot start method and a hot start device for an internal combustion engine. According to the teaching disclosed in said publication, a hot start situation is assumed to exist when the engine temperature and the air intake temperature exceed certain threshold values and, moreover, the absolute-value difference between the air intake temperature at an earlier point in time and the air intake temperature during restart is above a selectable threshold.
Publication DE 44 35 419 A1 discloses a control system for the fuel metering of an internal combustion engine. In this case, a hot start situation is assumed to exist and an appropriate hot start bit is set when the temperature of the internal combustion engine exceeds an initial threshold and, in addition to this, the air intake temperature has increased by a certain amount since a last measurement. The last value can be the one that existed at the instant when the internal combustion engine was shut down, and the new value can have been obtained at the instant when the ignition or the starter was switched on. The hot start bit remains set until the internal combustion engine temperature exceeds a second threshold, or until a predetermined total air mass has flowed through the intake manifold. Said total air mass is detected by integrating the signal of an air mass sensor in the intake manifold.
In the case of modern fuel injection systems that operate with high-pressure fuel injection in particular, some components, e.g., the high-pressure pump, heat up substantially slower than the coolant of the internal combustion engine. It is therefore possible, after the internal combustion engine has been shut off, for the coolant temperature to have already dropped or to drop compared to the shut-off temperature, while the temperature of the high-pressure pump and other components is still high and/or increases even further.